On the age of the Surakian and Inoceramian stages
Abstract
Chekanovsky, during his trip to the Olenek in 1875, established for the Mesozoic deposits developed along the Olenek and Lena two divisions, which he named: the lower (dark clayey shales with Inoceramus retrorsus) — the Surak stage, and the upper (light gray sandstones with I. retrorsus and aucellae) — the Inoceramian stage. The first mention of this is in the article by Lagusen, who described the fauna of these deposits and came to the conclusion that in age they can be compared with the Volgian stages, and the Inoceramian stage is apparently even younger than the upper Volgian stage. Later, D. N. Sokolov, in connection with the question of the age of I. retrorsus, recognized that the Surak stage corresponds to the upper part of the upper Volgian stage or the Berriasian; but he was inclined to consider the Inoceramian stage to be merely a facies change of the Surak stage, differing from it in the co‑occurrence of inoceramids and aucellae, or even in the predominance of the latter. The idea of the position of both Chekanovskii’s stages at the Jurassic‑Cretaceous boundary or at the very bottom of the Lower Cretaceous was accepted by all subsequent authors and transferred to summary works on the geology of Siberia.
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References
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